As poisons go, polonium-210 is a bit of a mixed bag. Is it effective? Absolutely. If you eat a piece of polonium-210 the size of a grain of salt, it'll probably be enough to kill the average adult. That said, the highly unstable element is notorious for leaving an unmistakable calling card: ridiculously high levels of radiation in the bodies of its victims.

This incredibly dangerous isotope of Polonium, an element discovered by Marie and Pierre Curie over a century ago, recently caught the public's attention after an analysis of effects belonging to Yasser Arafat — who died of unknown causes in November 2004 — revealed them to be covered in abnormal levels of the isotope.

Over on Elemental, Deborah Blum weighs the pros and cons of polonium-210's use among assassins by exploring its chemistry, the history of its use, and the nature of its traceability. It's a fascinating, if morbid, read, and while we've included an excerpt of the post below, it's one we definitely recommend checking out in full.

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Writes Blum:

Like radium, polonium's radiation is primarily in the form of alpha rays - the emission of alpha particles. Compared to other subatomic particles, alpha particles tend to be high energy and high mass. Their relatively larger mass means that they don't penetrate as well as other forms of radiation, in fact, alpha particles barely penetrate the skin. And they can stopped from even that by a piece of paper or protective clothing.

That may make them sound safe. It shouldn't. It should just alert us that these are only really dangerous when they are inside the body. If a material emitting alpha radiation is swallowed or inhaled, there's nothing benign about it. Scientists realized, for instance, that the reason the Radium Girls died of radiation poisoning was because they were lip-pointing their paintbrushes and swallowing radium-laced paint. The radioactive material deposited in their bones - which literally crumbled. Radium, by the way, has a half-life of about 1,600 years. Which means that it's not in polonium's league as an alpha emitter. How bad is this? By mass, polonium-210 is considered to be about 250,000 times more poisonous than hydrogen cyanide.

In other words, a victim would never taste a lethal dose in food or drink. In the case of Litvinenko, investigators believed that he received his dose of polonium-210 in a cup of tea, dosed during a meeting with two Russian agents. (Just as an aside, alpha particles tend not to set off radiation detectors so it's relatively easy to smuggle from country to country.) Another assassin advantage is that illness comes on gradually, making it hard to pinpoint the event. Yet another advantage is that polonium poisoning is so rare that it's not part of a standard toxics screen. In Litvinenko's case, the poison wasn't identified until shortly after his death. In Arafat's case - if polonium-210 killed him and that has not been established - obviously it wasn't considered at the time. And finally, it gets the job done. "Once absorbed," notes the U.S. Regulatory Commission, "The alpha radiation can rapidly destroy major organs, DNA and the immune system."